Method of hemodilution facilitated by monitoring oxygenation status

Abstract

A method for hemodiluting a patient is disclosed which includes the steps of administering a biocompatible oxygen carrier in conjunction with surgery or organ ischemia or infarct while assessing the patient's PvO2 or other oxygenation indices, and administering to the patient additional oxygen carrier or autologous blood in response to the PvO2 value if necessary to maintain the PvO2 at or above the desired level.

Description

FIELD OF THE INVENTIONThe present invention relates to improved medical procedures involving hemodilution. The improved method includes the administration of an oxygen carrier, the continuous monitoring of the mixed venous partial pressure of oxygen (PvO.sub.2) or other tissue oxygenation indices, and the administration of autologous blood or additional oxygen carrier to maintain the PvO.sub.2 or other indices at or above a predetermined level.BACKGROUND OF THE INVENTIONMore than 13 million units of blood are collected each year in the United States alone, and about 10 million of these units are transfused into 4 million recipients. Of the transfused units, about two-thirds are used during surgical procedures, and the remainder are used primarily for treating severe anemia or in emergency indications. Experience from clinical studies suggests that postoperative recovery can be shortened if hemoglobin concentrations are not allowed to fall to below 10 g / dL, the previously generally a...

AI Technical Summary

Benefits of technology

In general, improvement of blood fluidity by hemodilution has been shown to increase mean tissue PO.sub.2 in various organs (Messmer et al. Res. Exp. Med. 159:152-56 (1973)). This increase in tissue PO.sub.2 was attributed to more even flow distribution at the microcirculatory level and was interpreted as improved tissue oxygenation. On the other hand, Homer Microvasc. Res. 22:308-23 (1981), argued that in acute anemia there may be large differences between red blood cell PO.sub.2 and the plasma PO.sub.2. This would occur as a result of O.sub.2 diffusion from the red cell being slowed by passage through the plasma (which has very low O.sub.2 solubility characteristics). With hemodilution, the spacing between red blood cells in tissue capillaries is increased so that outward diffusion of O.sub.2 from red cells is slowed further by the increased diffusional barrier of plasma. The resultant gradient for PO.sub.2 may not be resolved (i.e., not all the oxygen has time to unload) during the short time that the red cell dwells in the capillary and O.sub.2 extraction may be diminished accordingly (Gutierrez, Respirat. Physiol. 63:79-96 (1985)).

Problems solved by technology

Despite an increased awareness and acceptance of the benefits of autologous blood transfusion, recent studies have revealed the widespread underutilization of autologous predonation (which is estimated to represent only 2-5% of all units drawn nationwide).

The use of such blood substitutes in large volumes to replace blood used in transfusions has not been entirely satisfactory in earlier applications.

For example, early studies using FLUOSOL as a large volume blood substitute found that following blood loss, FLUOSOL was "unnecessary in moderate anemia and ineffective in sever anemia."

Thus, it was concluded that use of fluorocarbon emulsions as blood substitutes would not provide a significant benefit in severely anemic and bleeding patients.

Indeed, although the U.S. Food & Drug Administration approved FLUOSOL in 1989 for use as a perfusion agent to enhance myocardial oxygenation during percutaneous transluminal coronary angioplasty (PTCA), it did not approve an earlier application for use as a large volume blood substitute for general use.

The problem in using fluorocarbon emulsions and hemoglobin compositions as red cell substituted or blood substitutes to compensate for blood loss from surgery, disease, or trauma lies in the relatively short circulating blood half life of those materials in vivo.

Thus, even if sufficient quantities of a red cell substitute are administered during and / or after surgery, for example, to provide adequate oxygen delivery, the oxygen carrying capacity will drop significantly long before the body can compensate by making new red cells.

Under no circumstance during current treatment methods is blood purposefully diluted, as this would dilute the concentration of red blood cells and thus impair the delivery of oxygen to the hearts.

Many cellular elements of blood, however, are detrimental in the case of myocardial infarction.

Hemodilution is not done, however, because it is also necessary to maintain high red blood-cell levels to deliver oxygen to the myocardium.

Images